Final Fantasy Record Keeper

Debuff Vulnerabilities
None

Abilities
► Phase 1
Dragon Fang: Deal physical damage twice to one target.
Firestorm: Deal special wind damage to all targets.
Flare: Deal massive non-elemental damage to one target.
Megaflare: Deal moderate non-elemental damage to all targets.
Gigaflare: Deal very heavy non-elemental damage to all targets.

► Phase 2

Tail: Deal moderate physical damage to one target.
Dragon Fang: Deal physical damage twice to one target.
Lunge: Deal ranged physical damage to all targets.
Firestorm: Deal special wind damage to all targets.
Flare: Deal massive non-elemental damage to one target.
Megaflare: Deal moderate non-elemental damage to all targets.
Gigaflare: Deal very heavy non-elemental damage to all targets.
Gigaflare (Nightmare): Deal fixed non-elemental damage to all targets. (5555 fixed + 1111 per “consumed” Energy Sphere)
Megaflare (Counter): Deal moderate non-elemental damage to all targets. (trigger: physical attacks, black & white magic)

► Phase 3

Lunge: Deal ranged physical damage to all targets.
Flare: Deal massive non-elemental damage to one target.
Megaflare: Deal moderate non-elemental damage to all targets.
Gigaflare: Deal very heavy non-elemental damage to all targets.
Gigaflare (Nightmare): Deal fixed non-elemental damage to all targets. (5555 fixed + 1111 per “consumed” Energy Sphere)

► Energy Sphere

Energy Bullet: Deal special non-elemental damage to one target.
Energy Bullet: Deal moderate special non-elemental damage to one target.
Energy Bullet: Deal heavy special non-elemental damage to one target.

Strategy
(special mention: tfmurphy, Lanaka7, Palisy, Zurai001)
PHASE 1 (100%-80%):
No special mechanics in this phase. Just beat the boss down until Phase 2 starts. One thing worth noting is that you can use Ninja or White Magic abilities to deal damage in Phase 1. This lets you save some summon uses for Phase 2 and 3 which are the critical phases.

PHASE 2 (79%-50%):

Neo Bahamut gains Reflect at the start of this phase.
You’ll notice the background will change. This changes throughout Phase 2 and it will indicate the element Neo Bahamut is currently weak to and also what element it currently resists (this is important).
Red fiery background (Fire stage): Weak to Ice; Resists Fire
Blue icy background (Ice stage): Weak to Fire; Resists Ice
Stormy grassfield background (Lightning stage): Weak to Water; Resists Lightning
After every two turns, the background will change. Background cycle is as follows: F → I → L → F → I → L (in other words after 12 turns have elapsed, if Neo Bahamut’s HP isn’t brought down to 50% yet, Phase 2 ends prematurely and Phase 3 will begin)
IMPORTANT: If you use an element that Bahamut resists, an Energy Sphere will spawn, they are immune to damage. Energy spheres come in 3 main colours: Red, Blue, Yellow (using a fire summon when Bahamut is currently resisting fire elements will spawn a Red Energy Sphere, and so on). Note that ONLY SUMMONS will trigger Energy Sphere spawns. (using Ninja abilities won’t work)
Energy Spheres have three “Levels” of power, and they are indicated by its size. Power levels are determined by damage you deal from summons: 1-3999 = Level 1; 4000-9999 = Level 2; 10000 and above = Level 3.
(So let’s say in the Fire stage, Ifrit deals 2.5k per hit, the Energy Sphere spawned will be Level 2.)
You can spawn multiple Energy Spheres (maximum of 3 Spheres). You can only spawn 1 Sphere for each element. (You cannot spawn 2 Red Spheres, for instance)
You need to have at least one Energy Sphere spawned before going into Phase 3.
PHASE 3 (49%-0%):

Energy Spheres become targetable now. They have an invisible timer. If the timer runs out and the Spheres are still alive, it is a wipe.
If you destroy Spheres within the timer, the Spheres will damage Bahamut. A Level 1 Sphere will deal 1×9999 damage to Bahamut; Level 2 = 2×9999; and Level 3 = 3×9999
Therefore, the more Spheres you spawn in P2, and the more times you charge it, then you’ll have a very quick P3 (assuming you are able to nuke all Spheres down in time)
Other than that, it’s a race to the finish line. Neo Bahamut will be spamming Gigaflare a lot.
Energy spheres must be destroyed with a Summon attack. Failure in doing so will trigger Gigaflare NIghtmare.
If there are multiple Energy Spheres, all of them has to be defeated simultaneously. If one Sphere is defeated before the other(s), all other Spheres will be consumed, and any Spheres that are alive will trigger Gigaflare Nightmare.